Moderate Dispersion Spectra of NH2 in Comet Hale-Bopp: Analysis of Population Distribution in $\widetilde X^{2} \textrm B_{1}(0,0,0)$ State of NH 2

Abstract

We carried out moderate-dispersion spectroscopic observations of comet Hale-Bopp (C/1995O1) on 1997 February 25, in order to study the fine structure of two NH 2 emission bands, $\widetilde A(0,9,0)-\widetilde X(0,0,0)$ and $\widetilde A(0,8,0)-\widetilde X(0,0,0)$ , which was resolved in our spectra. We compared the observed fine structure with that of the modeled spectra, which were computed based on the transition probabilities of NH 2 between the $\widetilde A(0,v^{\prime}_{2},0)$ and $\widetilde X(0,0,0)$ states determined by ourselves. From a comparison between the observation and the calculations we concluded that the population distribution of the NH 2 in the $\widetilde X(0,0,0)$ ground state can be approximated by the Boltzmann distribution at a temperature of 60 K.

Vibronic transition moments and line intensities for H2O+

“…The ab initio results were used to generate parameterized analytical representations of the electronic dipole moments and the transition moment, and the parameter values were used as input for the RENNER program system (see [22] and references therein) in calculations producing vibronic transition moments and line strengths for individual rovibronic transitions in theX -X andÃ-X band systems of H 2 O þ . The calculation of vibronic transition moments is analogous to that reported recently [23] for the isoelectronic molecule NH 2 ; this latter calculation served to assist the simulation of cometary spectra [24] originating in theX -X andÃ-X band systems of NH 2 and observed in the comets Hale-Bopp and C/ 1994 S4 (LINEAR) [25][26][27]. From the ortho-to-para ratio determined in the analysis of the NH 2 spectra it is possible, by a complicated chain of reasoning, to determine the distance from the solar nebula to the point where the comet was formed [25][26][27].…”

“…The calculation of vibronic transition moments is analogous to that reported recently [23] for the isoelectronic molecule NH 2 ; this latter calculation served to assist the simulation of cometary spectra [24] originating in theX -X andÃ-X band systems of NH 2 and observed in the comets Hale-Bopp and C/ 1994 S4 (LINEAR) [25][26][27]. From the ortho-to-para ratio determined in the analysis of the NH 2 spectra it is possible, by a complicated chain of reasoning, to determine the distance from the solar nebula to the point where the comet was formed [25][26][27].…”

“…We have calculated the T(K 0 ; C 0 rve ; K 00 ; C 00 rve ) matrices with a basis set (see, for example [23]) having (N 00 bend , N 0 bend , N 00 stretch , N 0 stretch , N 00 (18,14,12,12,31,12,25,9). We limited the output from the calculation to give only matrix elements with absolute values larger than 10 À3 D. Of these matrix elements, we listed only those involving wavefunctions whose dominant contribution is from basis functions with N 00 bend , N 0 bend 6 14, and from the five stretching basis functions of lowest energy with A 1 or B 2 symmetry.…”

High polarization degree of the continuum of comet 2P/Encke based on spectropolarimetric signals during its 2017 apparition

“…To identify the wavelengths and intensities of molecular emissions, we calculate the distribution of fluorescent lines in optical wavelengths (0.4-1.0 µm) at the sppol observing geometry of 2P, and we use the fluorescence excitation models of C 2 (Shinnaka et al 2010), NH 2 (Kawakita et al 2000), and CN (Shinnaka et al 2017). In the NH 2 model, we assume the fluorescence equilibrium condition and fix an ortho-to-para abundance ratio of 3.2, which is a typical value found in comets (Shinnaka et al 2016).…”

Ab initio potential energy surface, electric-dipole moment, polarizability tensor, and theoretical rovibrational spectra in the electronic ground state of

“…For example, the nascent ortho-topara ratio (OPR) for NH 3 in a comet can be interpreted to give the temperature of formation of the NH 3 species, and hence the temperature of formation of the comet; the temperature of formation of the comet indicates the distance from the solar nebula at which the comet was formed. The NH 3 OPR can be determined by analysis of the emission spectrum of NH 2 which derives from the photodissociation of NH 3 [40][41][42]. Interstellar microwave transitions have already been observed for NH 3 [37].…”